How to Disinfect Water with Bleach

The short answer

Boiling is the CDC’s preferred way to kill germs. When boiling is not possible, use only plain, unscented household liquid bleach that lists sodium hypochlorite as its active ingredient and has no added cleaners or fragrances. Follow drinking-water directions on the label. If none are provided, use the CDC table below for bleach containing 5%–9% sodium hypochlorite.

Before measuring anything

1. Rule out chemical contamination. If chemicals, fuel, saltwater, or toxins may be present, do not use the water.
2. Find the concentration. Read the active-ingredient panel for the percentage of sodium hypochlorite.
3. Use the correct product. Do not use scented, color-safe, gel, splashless, powdered, or bleach with added cleaners unless its label specifically gives drinking-water disinfection directions.
4. Clarify the water. If cloudy, let particles settle and pour the clearer water through a clean cloth, paper towel, or coffee filter.

CDC emergency ratios for 5%–9% bleach

Use the cloudy-water amount when the water is cloudy, murky, colored, or very cold—even after pre-filtering.

Why “eight drops per gallon” is not the whole rule

Eight drops is the CDC’s practical dose for one gallon of clear water when ordinary household bleach contains 5%–9% sodium hypochlorite. EPA’s table distinguishes 6% and 8.25% products, and substantially weaker products need a different dose. That is why the label and concentration must come before the number.

What bleach can—and cannot—do

Correct chlorination can kill many disease-causing bacteria and viruses. It is less effective against some parasites, including Cryptosporidium. It does not remove sediment, salt, lead, arsenic, pesticides, petroleum products, or other dissolved chemicals. When boiling is available, the CDC recommends bringing clear water to a rolling boil for one minute, or three minutes above 6,500 feet.

Safe handling

• Work in a ventilated area and avoid splashes to eyes, skin, and clothing.
• Never mix bleach with ammonia, vinegar, acids, or another cleaner; dangerous gas can form.
• Keep bleach in its original labeled container, tightly closed, away from heat and sunlight.
• Use a clean dropper reserved for this purpose and never return measured bleach to the bottle.
• Bleach loses strength over time. EPA recommends fresh liquid bleach or bleach stored at room temperature for less than one year.

Common mistakes

Using teaspoons without checking the volume

For a single gallon, drops or milliliters are more precise. “One-eighth teaspoon” is an approximation; the CDC describes the 5%–9% dose as slightly less than 1/8 teaspoon.

Disinfecting visibly dirty water without clarifying it

Particles can interfere with treatment. Let water settle and filter the clearer portion first, then use the doubled dose if it remains cloudy, colored, or very cold.

Assuming a chlorine smell proves every hazard is gone

A slight odor is part of the emergency disinfection check, but it does not show that chemicals, salt, metals, or all parasites were removed.

Using the sanitation ratio for drinking water

The stronger bleach solution used to sanitize an empty storage container is not the drinking-water dose. Keep the two procedures separate.

Frequently asked questions

How much 6% bleach goes into one gallon of clear water?

EPA guidance lists 8 drops. Stir and wait 30 minutes.

How much 8.25% bleach goes into one gallon?

EPA guidance lists 6 drops for clear water. Double the dose if the water is cloudy, colored, or very cold.

Can I use 1% bleach?

CDC provides a separate ratio: 40 drops, 2.5 mL, or 1/2 teaspoon per gallon of clear water. Do not substitute the 5%–9% table for a 1% product.

Can bleach make floodwater safe?

Do not assume so. Floodwater may contain sewage plus fuels, pesticides, metals, and industrial chemicals. Use a known-safe source whenever possible and follow authorities.

Sources

Ratios, contact times, cloudy-water adjustments, boiling directions, and treatment limits follow CDC emergency-water guidance and the EPA emergency disinfection table.